linux-kernel - Re: [PATCH v2] dma-mapping: use vmalloc_to

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Message-ID: <CADu_u-MxpRVm92yL_d0mWS06KBv_dv6jJ+OHt8KdjsSup_0j5g@mail.gmail.com>
Date:   Thu, 15 Jul 2021 10:31:36 +0300
From:   Roman Skakun <rm.skakun@...il.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        xen-devel@...ts.xenproject.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Volodymyr Babchuk <volodymyr_babchuk@...m.com>,
        Roman Skakun <roman_skakun@...m.com>,
        Andrii Anisov <andrii_anisov@...m.com>
Subject: Re: [PATCH v2] dma-mapping: use vmalloc_to_page for vmalloc addresses

Hi, Stefano!

> We have the same thing in xen_swiotlb_free_coherent. Can we find a way
> to call cpu_addr_to_page() from xen_swiotlb_free_coherent?
> Maybe we can make cpu_addr_to_page non-static?

Yes, right, If we want to reuse this helper instead of the same code
block in xen_swiotlb_free_coherent() need to make cpu_addr_to_page() as
global and add a new declaration for this helper in include/linux/dma-map-ops.h.
What do you think?

Cheers!

ср, 14 июл. 2021 г. в 04:23, Stefano Stabellini <sstabellini@...nel.org>:
>
> On Tue, 22 Jun 2021, Roman Skakun wrote:
> > This commit is dedicated to fix incorrect conversion from
> > cpu_addr to page address in cases when we get virtual
> > address which allocated in the vmalloc range.
> > As the result, virt_to_page() cannot convert this address
> > properly and return incorrect page address.
> >
> > Need to detect such cases and obtains the page address using
> > vmalloc_to_page() instead.
> >
> > Signed-off-by: Roman Skakun <roman_skakun@...m.com>
> > Reviewed-by: Andrii Anisov <andrii_anisov@...m.com>
> > ---
> > Hey!
> > Thanks for suggestions, Christoph!
> > I updated the patch according to your advice.
> > But, I'm so surprised because nobody catches this problem
> > in the common code before. It looks a bit strange as for me.
> >
> >
> >  kernel/dma/ops_helpers.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/dma/ops_helpers.c b/kernel/dma/ops_helpers.c
> > index 910ae69cae77..782728d8a393 100644
> > --- a/kernel/dma/ops_helpers.c
> > +++ b/kernel/dma/ops_helpers.c
> > @@ -5,6 +5,14 @@
> >   */
> >  #include <linux/dma-map-ops.h>
> >
> > +static struct page *cpu_addr_to_page(void *cpu_addr)
> > +{
> > +     if (is_vmalloc_addr(cpu_addr))
> > +             return vmalloc_to_page(cpu_addr);
> > +     else
> > +             return virt_to_page(cpu_addr);
> > +}
>
> We have the same thing in xen_swiotlb_free_coherent. Can we find a way
> to call cpu_addr_to_page() from xen_swiotlb_free_coherent? Maybe we can
> make cpu_addr_to_page non-static? No problem if it is too much trouble.
>
>
> >  /*
> >   * Create scatter-list for the already allocated DMA buffer.
> >   */
> > @@ -12,7 +20,7 @@ int dma_common_get_sgtable(struct device *dev, struct sg_table *sgt,
> >                void *cpu_addr, dma_addr_t dma_addr, size_t size,
> >                unsigned long attrs)
> >  {
> > -     struct page *page = virt_to_page(cpu_addr);
> > +     struct page *page = cpu_addr_to_page(cpu_addr);
> >       int ret;
> >
> >       ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
> > @@ -43,7 +51,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
> >               return -ENXIO;
> >
> >       return remap_pfn_range(vma, vma->vm_start,
> > -                     page_to_pfn(virt_to_page(cpu_addr)) + vma->vm_pgoff,
> > +                     page_to_pfn(cpu_addr_to_page(cpu_addr)) + vma->vm_pgoff,
> >                       user_count << PAGE_SHIFT, vma->vm_page_prot);
> >  #else
> >       return -ENXIO;
> > --
> > 2.25.1
> >



-- 
Best Regards, Roman.